单选题 A transport layer protocol has several responsibilities, One is to create a process-to-process (program-to-program) communication; TCP uses port ______ to accomplish this. Anotherresponsibility of a transport layer protocol is to create a ______ and error-control mechanism atthe transport level. TCP uses a sliding ______ protocol to achieve flow control. It uses theacknowledgment packet, time-out, and retransmission to achieve ______ control. The transportlayer is also responsible for providing a connection mechanism for the application program. Theapplication program sends ______ of data to the transport layer. It is the responsibility of thetransport layer at the sending station to make a connection with the receiver.